The present invention relates to an optically amplified transmission apparatus and a repeater of a remote pumping type in an optical two-way transmission system, for example. Particularly, the present invention relates to an optical transmitting apparatus and an optical repeating apparatus suitable for use in a system which can transmit transmission-reception light and pumping light through optical fiber cables in one system, remotely control the output level of a pumping source, fulfil an optical level controlling function, a disconnect detecting function and an automatic restoring function for an optical cable among the stations.
Long distant transmission using optical fiber cables (hereinafter referred as optical cables, occasionally) is performed in order to transmit a large volume of data at a high speed, in recent years. In the long distance transmission, a transmission loss generates in an optical cable. For this, the optically amplified transmission system transmits transmission light and reception light through different optical cables in order to compensate it.
The optically amplified transmission system can remotely control an amplification level of an optical amplifier in the optical repeater. When the optical cables are installed undersea, for example, it is possible to remotely adjust the amplification level using an optical cable instead the administrator adjusts the amplification level by hands. Concretely, this adjustment is carried out by inputting pumping light to the optical amplifier, which is called the optical pumping system. In the optical pumping system, the pumping light of a transmission path terminal station is transmitted to an optical repeater, the transmitted pumping light and transmission light are multiplexed in the optical repeater, whereby optical repeating is performed.
In order to perform the optical repeating, a different optical cable from optical cables through which the transmission light and the pumping light are transmitted is installed, and these optical cables are prepared for each repeater to transmit optical signals. These repeaters are connected by the optical cables.
When a fault occurs in the optical cable and the optical cable is cut, it is necessary to specify the cut position and restore it. Detection of cut of an optical cable is called disconnect detection of an optical cable. The disconnect detecting function is dispensable.
FIG. 47 is a diagram showing an example of the optically amplified transmission system using the remote pumping optically amplifying system. An optically amplified transmission system 90 shown in FIG. 47 is described in Japanese Patent Laid-Open Publication No. 9-113941 in which a technique is disclosed, which can further extend a transmission distance of optical signals using an optically amplifying system which can do remote pumping.
The optically amplified transmission system 90 shown in FIG. 47 comprises a transmitting station (transmitting terminal) 90a, a receiving station (receiving terminal) 90b, a plurality (three, for example) of repeating stations 90c, and a plurality (three, for example) of repeating stations 90d between them. Optical cables in two systems are used for transmission and reception.
The transmitting station 90a comprises a transmitting unit 91a and a receiving unit 91b. The receiving station 90b comprises a transmitting unit 91d and a receiving unit 91c, as well. The transmitting unit 91a and the receiving unit 91d comprise a signal light source 92a and a plurality of pumping sources 92b. Each of the transmitting station 90a and the receiving station 90b prepares the pumping sources 92b in different systems from that of the signal light source in order to perform remote pumping, whereby pumping light is transmitted from a terminal station to a repeater through an optical cable differing from an optical cable for transmission-reception light between the transmitting station 90a and the receiving station 90b. 
Japanese Patent Laid-Open Publication No. 9-200144 discloses an optically amplified repeating system which can suppress the output level of a repeater apparatus to realize a long repeater spacing. According to the technique disclosed in this publication, it is possible to extend the repeating distance.
However, the techniques disclosed in Japanese Patent Laid-Open Publication No. 9-113941 and Japanese Patent Laid-Open Publication No. 9-200144 have three types of problems. First, since a plurality of pumping sources are transmitted through optical cables differing from an optical cable through which optical signals are transmitted, the investment cost of the optical cables is high. In concrete, in the optically amplified transmission system 90 shown in FIG. 47, the number of the optical cables required among the optical repeaters is two to three, and the number of optical cables required between the terminal stations is 14 for both transmission and reception. Further, no description of the optical level controlling method is seen therein.
Further, in remote pumping, adjustment of the output level between the optical repeaters sometimes lacks accuracy since the adjustment is carried out on the basis of theoretical optical transmission distance calculation. The second problem is that a precise control is necessary in each terminal station, which requires a labor cost of an administrator who executes the control.
The third problem is that the method for detecting cut of an optical cable is not established.
In the light of the above problems, the first object of the present invention is to enable transmission and reception of transmission light and reception light through one optical fiber cable, thereby decreasing the installation cost and maintenance cost of the optical cables.
The second object of the present invention is to detect cut of the optical cable by a monitoring function using pumping light and residual pumping light, thereby largely improving reliability and safety of the system. The third object of the present invention is to most suitably set optical output level adjustment in the repeating station according to an actual transmitting distance.
For this, an optical transmitting apparatus of this invention comprises an optical transmitting means for multiplexing and amplifying first transmission light (xcex1L) and first pumping light (xcex2PL) amplifying the first transmission light (xcex1L), and outputting amplified optical signal to an internal optical fiber, a level monitoring means connected to the optical transmitting means for detecting a level of the optical signal outputted from the optical transmitting means, an optical multiplexing means connected to the internal optical fiber for transmitting an optical signal in the internal optical fiber to a first optical fiber connected to an external optical repeating apparatus, and also being operable to receive an optical signal having a predetermined wavelength in transmission light transmitted from the external optical repeating apparatus through the first optical fiber, and split the optical signal into a plurality of directions, and output split optical signal, and a loop back light detecting means connected to the optical multiplexing means for receiving an optical monitoring signal (xcex2PLxe2x80x2) transmitted from the external optical repeating apparatus.
Accordingly, transmission light and reception light can be transmitted through optical fiber cables in one system, so that the installation cost and maintenance cost of an optical cable cost can be decreased. Since cut of the optical cable is performed by a monitoring function using pumping light and residual pumping light in a two-way transmission, reliability and safety of the system can be remarkably improved.
An optical repeating apparatus of this invention comprises a first optical transmitting means for receiving first transmission light (xcex1L) and first pumping light (xcex2PL) transmitted from an optical transmitting apparatus through a first optical fiber, amplifying the first transmission light (xcex1L) and the first pumping light (xcex2PL), and outputting second transmission light (xcex1Lxe2x80x2) and second pumping light (xcex2PLxe2x80x2), a first loopback means connected to the first optical transmitting means to extract the second pumping light (xcex2PLxe2x80x2) from the optical signal amplified by the first optical transmitting means, and outputting the second pumping light (xcex2PLxe2x80x2), a second optical transmitting means for receiving third transmission light (xcex1R) and third pumping light (xcex3PR) transmitted from an optical receiving apparatus through the second optical fiber, amplifying the third transmission light (xcex1R) and the third pumping light (xcex3PR), and outputting fourth transmission light (xcex1Rxe2x80x2), a second loopback means connected to the second optical transmitting means to extract fourth pumping light (xcex3PRxe2x80x2) from the optical signal amplified by the second optical transmitting means, and outputting the fourth pumping light (xcex3PRxe2x80x2), a first optical coupler disposed on an output""s side of the first optical transmitting means to output the second transmission light (xcex1Lxe2x80x2) and the second pumping light (xcex2PLxe2x80x2) toward the optical receiving apparatus, while outputting the third transmission light (xcex1R) and the third pumping light (xcex3PR) from the optical receiving apparatus, and a second optical coupler disposed on an output""s side of the second optical transmitting means to output the optical signal from the first loopback means and the optical signal from the second optical transmitting means toward a side of the optical transmitting apparatus, while outputting the first transmission light (xcex1L) and the first pumping light (xcex2PL) from a side of the optical transmitting apparatus.
Accordingly, optical output level adjustment in the repeating station is most suitably set according to an actual transmission distance, which allows an efficient system operation.